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Troubleshooting Common WP File Manager Errors: From Blank Screens to PHP 8 Fatal Errors

59 threads Sep 16, 2025 Plugin → File manager

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WP File Manager is a powerful tool for managing your WordPress site's files directly from the admin dashboard. However, like any complex plugin, users can occasionally encounter errors. Based on community reports and troubleshooting threads, this guide covers some of the most common WP File Manager issues and their solutions.

1. Blank White Screen (White Screen of Death)

The Problem: After updating WP File Manager or WordPress itself, you may find that your /wp-admin area or the plugin interface becomes a blank white screen.

Why It Happens: This is often caused by a PHP error that is being hidden by your site's default configuration. Incompatibilities with your current PHP or WordPress version can also be the culprit.

How to Fix It:

  1. Enable Debugging: Temporarily enable WordPress debugging by adding the following lines to your wp-config.php file. This will often reveal the specific error causing the blank screen. 
    define( 'WP_DEBUG', true );
define( 'WP_DEBUG_LOG', true ); // Logs errors to wp-content/debug.log
define( 'WP_DEBUG_DISPLAY', false ); // Prevents errors from being printed on screen
  2. Check Compatibility: Ensure your WordPress, PHP, and WP File Manager versions are all compatible. Older plugin versions may not work with newer PHP versions (like PHP 8.0+).
  3. Update the Plugin: If you can access your admin area after disabling other plugins, check for an update to WP File Manager. Many compatibility issues are patched in subsequent releases.

2. PHP Fatal Errors on PHP 8.0+

The Problem: After upgrading your server to PHP 8.0 or later, your site crashes with a fatal error, often mentioning that a function like fclose() expects a resource but was given a boolean.

Why It Happens: PHP 8 introduced stricter type checking for functions. Older code that did not properly check if a file operation (like fopen()) was successful before trying to use the result will now throw a fatal error.

How to Fix It:

  1. Roll Back PHP Version (Temporary Fix): If your site is critical, contact your hosting provider to temporarily switch back to PHP 7.4 until a permanent fix is implemented.
  2. Update the Plugin: The File Manager team has addressed these PHP 8 compatibility issues in newer versions. Updating to the latest available version of the plugin is the recommended solution.

3. "Invalid Backend Response" or "Data is not JSON" Errors

The Problem: When trying to edit, create, or delete files, the operation fails with an "Invalid backend response" error. This may also manifest as a spinning loading icon when trying to open a folder with a very large number of files (e.g., wp-content/uploads).

Why It Happens: This is typically a server-level issue. It can be caused by a configuration that limits script execution time or memory, a server module (like mod_security) blocking the request, or the server timing out while trying to process a directory with thousands of files.

How to Fix It:

  1. Check Server Error Logs: Your hosting provider should give you access to server error logs (e.g., in cPanel > Metrics > Error Logs). These logs often contain more detailed information about what caused the 502 or 503 error.
  2. Increase PHP Limits: Try increasing the PHP memory limit and maximum execution time. You can often do this by adding the following to your wp-config.php file above the line that says /* That's all, stop editing! Happy publishing. */. 
    define( 'WP_MEMORY_LIMIT', '256M' );
set_time_limit( 300 );
    Warning: Edit this file carefully. A syntax error (like a missing semicolon or quote) will break your site. If this happens, you will need to use your hosting provider's file manager or FTP to correct the mistake.
  3. Contact Your Host: If the problem persists, particularly the 502 error on large directories, your host may need to adjust server configuration settings like fastcgi_read_timeout.

4. File Permission and Ownership Issues

The Problem: You cannot update, delete, or rename the WP File Manager plugin itself, often because the plugin's folder has unusual ownership (e.g., showing as owner "0") or read-only permissions.

Why It Happens: This is almost always a server environment issue. If the plugin was installed or updated while WordPress was running under a different system user (e.g., during a manual update via FTP), it can lead to a permissions mismatch.

How to Fix It:

  1. Use Your Host's File Manager or FTP/SSH: The free version of WP File Manager does not include functionality to change file permissions or ownership. You will need to use your hosting provider's control panel file manager or an FTP/SFTP client like FileZilla to correct the permissions. The standard permission for WordPress folders is 755 and for files is 644.
  2. Contact Your Hosting Provider: If you are unsure how to change permissions or ownership, your hosting provider's support team can assist you with this server-level task.

General Troubleshooting Tips

  • Plugin Conflict Test: Many strange issues, like blank text areas or missing menus, are caused by conflicts with other plugins. Deactivate all other plugins and see if the problem resolves. If it does, reactivate them one by one to identify the culprit.
  • Check for Known Issues: Before making changes, search the WordPress.org support forums for WP File Manager to see if others have reported the same issue and found a solution.

Remember, when editing critical files like wp-config.php or using a file manager plugin, always create a backup first. Many hosting providers offer this functionality within their control panel.

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